Related automotive paint compositions of this type are disclosed in U.S. patent applications titled METALLIC WATER BORNE BASE COAT COMPOSITION BASED ON ACRYLIC LATEX RESINS USING A WATER REDUCIBLE RESIN FOR ALUMINUM STORAGE AND A PREGELLED HECTRORITE CLAY FOR RHEOLOGY CONTROL Ser. No. 07/553065 filed Sep. 10, 1990 ABN Sep. 18, 1992, METALLIC WATER BORNE BASE COAT COMPOSITION BASED ON ACRYLIC LATEX RESINS USING A WATER REDUCIBLE RESIN FOR ALUMINUM STORAGE AND A TREATED HECTORITE CLAY FOR RHEOLOGY CONTROL Ser. No. 07/553063 filed Jul 13, 1990 ABN Sep. 18, 1992. METALLIC WATER BORNE BASE COAT COMPOSITION BASED ON ACRYLIC LATEX RESINS USING AN ACRYLIC RESIN HAVING ACID AND NONIONIC FUNCTIONALITY FOR ALUMINUM STORAGE AND A PREGELLED HETORITE CLAY FOR RHEOLOGY, CONTROL Ser. No. 07/554606 filed Sep. 10, 1990 now U.S. Pat. No. 5,166,255 , METALLIC WATER BORNE BASE COATE COMPOSITION BASED ON ACRYLIC LATEX RESINS USING AN ACRYLIC RESIN HAVING ACID AND NONIONIC FUNCTIONALITY FOR ALUMINUM STORAGE AND A TREATED HETORITE CLAY FOR RHEOLOGY CONTROL Ser. No. 07/553100 filed Sep. 10, 1990, METALLIC WATER BORNE BASE COAT COMPOSITION BASED ON ACRYLIC LATEX RESINS AND ACRYLIC RESINS DERIVED FROM ACRYLIC MONOMERS HAVING NONIONIC, URETHANE AND ACID FUNCTIONALITY FOR ALUMINUM STORAGE AND A PREGELLED HECTORITE CLAY FOR RHEOLOGY CONTROL Ser. No. 07/553069 filed Sep. 10, 1990, METALLIC WATER BORNE BASE COAT COMPOSITION BASED ON ACRYLIC LATEX RESINS AND ACRYLIC RESINS DERIVED FROM ACRYLIC MONOMERS HAVING NONIONIC, URETHANE AND ACID FUNCTIONALITY FOR ALUMINUM STORAGE AND A TREATED HECTORITE CLAY FOR RHEOLOGY CONTROL Ser. No. 07/553070 filed Jul. 13, 1990. METALLIC WATER BORNE BASE COAT COMPOSITON BASED ON ACRYLIC LATEX RESINS USING ACRYLIC RESINS DERIVED FROM VINYL MONOMERS HAVING NONIONIC AND URETHANE FUNCTIONALITY FOR ALUMINUM STORAGE AND A PREGELLED HECTORITE CLAY FOR RHEOLOGY CONTROL Ser. No. 07553066 filed Jul. 13, 1990, now abandoned, METALLIC WATER BORNE BASECOAT COMPOSITION BASED ON ACRYLIC LATEX RESINS USING ACRYLIC RESINS DERIVED FROM GRAFTING AN ISOCYANATE ADDUCT HAVING URETHANE AND NONIONIC FUNCTIONALITY ON TO AN ACRYLIC RESIN HAVING ACTIVE HYDROGEN FUNCTIONALITY FOR ALUMINUM STORAGE AND A PREGELLED HECTORITE CLAY FOR RHEOLOGY CONTROL Ser. No. 07/553064 filed Sep. 10, 1990, now abandoned, METALLIC WATER BORNE BASECOAT COMPOSITION BASED ON ACRYLIC LATE RESINS USING ACRYLIC RESINS DERIVED FROM GRAFTING AN ISOCYANATE ADDUCT HAVING URETHANE AND NONIONIC FUNCTIONALITY 0N TO AN ACRYLIC RESIN HAVING ACTIVE HYDROGEN FUNCTIONALITY FOR ALUMINUM STORAGE AND A TREATED HECTORITE CLAY FOR RHEOLOGY CONTROL Ser. No. 07/553068 filed Sep. 10, 1990, and ACRYLIC LATEX METALLIC WATER BORNE BASE COAT OF IMPROVED APPEARANCE Ser No. 07/355,959 filed May 23, 1989, now abandoned. All of these U.S. patents and applications are incorporated herein by reference.
It is customary in the painting of an automobile that a series of coatings be applied to the substrate. The first coat being the primer followed by the base coat and finally the clear coat. The base coat provides the good decorative quality to the final finish via organic and inorganic pigments. In many automobile finishes, a metallic finish is desired. To obtain this metallic effect, metallic pigments are present in the base coat, typically aluminum flakes. The aluminum flakes in the base coat contribute to the glossy lustrous appearance of the final finish.
Another feature that aluminum flakes contribute to the appearance of the final finish is the change of brightness as the viewing angle is changed. Typically, the final finish is bright when viewed at a 90 degree angle, however, when the viewing angle is changed to 180 degrees, the coating has a dark appearance. This phenomenon is known as "flop" in the automotive field and is highly desired. The ultimate in "flop" is achieved when the aluminum flakes are orientated parallel to the substrate. Random orientation of the aluminum flake results in a final finish exhibiting bright and dark areas when viewed at 90 degrees. This appearance is known as mottling and detracts from the final appearance of the final finish. In general, the metal fixation in base coats is achieved by a rheology modifiers such as inorganic and organic thickeners. The particular rheology control agent used in this invention results in a non-mottled, high head-on-brightness, outstanding flop, and high quality finish, even in the case of a silver metallic base coat. Also, use of this particular rheology control agent allows the coating to be applied wetter during the application process.
In the current market place, automobile coatings, especially base coats, contain a high level of organic solvent. With increasing concern about the volatile organic emissions into the atmosphere, an intensive effort in research and development of coatings containing mainly water as the solvent with a small level of organic solvent is under way. An example of such an effort is U.S. Pat. No. 4,730,020 which discloses a water-dilutable coating composition comprising specifically selected acrylic copolymers, solvent blends, coloring and/or optical effect pigments and polymer dispersions. To obtain the desired optical effect of the metallic flakes, the correct combination of acrylic copolymer and solvent blend must be achieved. An aqueous thermosetting acrylic resin described by U.S. Pat. No. 3,862,071 controls the metallic pigment orientation by the addition of a water insoluble copolymer. Microgel technology as described by GB-PS No. 2,073,609 also results in the proper metal orientation. Also disclosed in DE No. 3,210,051 is an attempt to control metallic pigment orientation using polyurethane dispersions. Cellulosic esters have also been used to control metal fixation as disclosed in DE No 3,216,549. The rheology modifiers or rheology control agents for water borne coatings have poor shelve stability, poor weathering characteristics and are cumbersome to use. The particular rheology control agent used in this invention results in a nonmottled, high head-on-brightness, outstanding flop, and high quality finish, even in the case of a silver metallic base coat and does not suffer from the problems cited earlier.
The use of acrylic latex resin in a base coat formulation has been disclosed in European Application 0 287 144 Al, however, this application does not disclose any rheology control agents, pigment dispersion procedures, method for aluminum storage and requires that the acrylic latex resin be prepared in 2 or more steps by emulsion polymerization.
Typically, coating compositions used in the automotive market, especially in the automotive after market, are produced by mixing various bases to give the desired color. These coating compositions are then applied in about 1-5 days after preparation. A major problem is the introduction of aluminum flakes which react with water to generate hydrogen gas. Therefore, the aluminum flake must be segregated from the rest of the water borne components to minimize this hazard.